The present invention relates to a technique effective to be applied to an electric component which is used in a wireless communication system such as a cellular phone and incorporates a high frequency power amplifier amplifying and outputting a high frequency transmitting signal and a power source circuit supplying operating voltage. More specifically, the present invention relates to a technique effective to be applied to an electric component for high frequency power amplifier configuring a wireless communication system in which phase modulation and amplitude modulation of a transmitting signal are performed separately to carry out control for the amplitude modulation in a high frequency power amplifier.
In general, a high frequency power amplifier amplifying a modulated signal is incorporated into an output part on the transmitting side in wireless communication equipment (mobile communication equipment) such as a cellular phone. To control the gain of the high frequency power amplifier in accordance with a transmission level required from a baseband circuit or a control circuit such as a microprocessor, the high frequency power amplifier or an output power detector detecting the output level of an antenna is provided to control the gain of the power amplifier based on output level indicating signal Vramp and the detected output from the output power detector (see Patent document 1).
As one of the recent communication systems in cellular phones, there is a cellular phone of the GSM (Global System for Mobile communication) system modulating a transmitting signal by GMSK modulation. In addition to the GMSK (Gaussian Minimum Shift Keying) modulation mode, a cellular phone of the system called EDGE (Enhanced Data Rates for GMS Evolution) having the 3π/8 rotating 8-PSK (Phase Shift Keying) modulation mode modulating the phase component and the amplitude component of a carrier wave and switching between the modes for performing communication is being put to practical use.
As a technique realizing the 3π/8 rotating 8-PSK modulation (hereinafter, called 8PSK modulation) of the EDGE system, there are a method of performing phase modulation at the previous stage of a power amplifier and performing amplitude modulation in the power amplifier (polar loop method), and a method of performing phase modulation and amplitude modulation in the previous stage of a power amplifier (Pin control method). The invention related to the cellular phone of the polar loop system is described in Patent document 2.
[Patent document 1] Japanese Unexamined Patent Publication No. 2000-151310
[Patent document 2] Japanese Unexamined Patent Publication No. 2004-007443